The present invention relates to a dispersion shifted optical fiber designed so that the chromatic dispersion value in a 1.55 xcexcm wavelength band where the loss of quartz based optical fiber is the smallest is substantially zero, and particularly to a dispersion shifted optical fiber having a large effective core area and a small dispersion slope
Conventionally, in a long distance system such as an optical amplification relay transmission system etc. that uses an optical fiber amplifier, in order to suppress deterioration in the transmission characteristics, it is vital that non-linear optical effects be reduced.
The size of the non-linear effect is represented by n2/Aeff. Here, n2 is the non-linear refractive index of an optical fiber and Aeff is the effective core area of the optical fiber. Accordingly, in order to reduce the non-linear effect, it is necessary to either reduce n2 or to increase the effective core area. However, because the value of n2 does not change greatly once the material thereof has been decided, the more effective method is to expand the effective core area for reducing the non-linear optical effect.
In a wavelength multiplex transmission system that is capable of large volume transmission, however, in order to transmit a plurality of optical signals having different wavelengths using a single dispersion shifted optical fiber (i.e. as a transmission path), there are increased demands for a reduction in the dispersion slope. The dispersion slope shows the wavelength dependency of the chromatic dispersion values and is a gradient of the curve when the chromatic dispersion values are plotted when the horizontal axis is set as the wavelength (nm) and the vertical axis is set as the chromatic dispersion values (ps/kmxc2x7nm).
The larger the dispersion slope of the dispersion shifted optical fiber, the larger the difference in the chromatic dispersion value between a plurality of wavelengths transmitted along one dispersion shifted optical fiber, the more irregular the transmission state, and the more the transmission characteristics are deteriorated. A large dispersion slope is therefore undesirable.
Further, the minimum conditions required for a transmission path for an optical communication system are that it is single mode essentially and that bending loss be held to 100 dB/m or less.
Therefore, recently, proposals intended to achieve a reduction in the dispersion slope and an enlargement in the effective core area using various refractive index distribution configurations (refractive index profiles) have been made in, for example, Japanese Patent Unexamined Application (JP-A) Nos. 10-293225, 10-239550, 11-119046, and the like.
FIGS. 5(a) to 5(d) show examples of the refractive index profile of such dispersion shifted optical fibers.
FIG. 5(a) shows an example of a step type (dual shape core type) of refractive index profile. A core 14 is formed provided with a central core portion 11 and a step core portion 12 provided at the outer periphery of the central core portion 11 and having a lower refractive index than the central core portion 11. In addition, cladding 16 having a lower refractive index than the step core portion 12 is provided at the outer periphery of the core 14.
FIG. 5(b) shows an example of a segment core type of refractive index profile. A core 24 is formed provided with a central core portion 21 having a high refractive index and an intermediate portion 22 having a low refractive index at the outer periphery of the central core portion 21. A ring core portion 23 having a lower refractive index than the central core portion 21 and a higher refractive index than the intermediate portion 22 is further provided at the outer periphery of the intermediate portion 22. In addition, cladding 26 having a refractive index equal to the intermediate portion 22 is provided at the outer periphery of the ring core portion 23.
FIG. 5(c) is a variant example of the step type refractive index profile shown in FIG. 5(a). A core 14 is formed with a low refractive index portion 15, which has a lower refractive index than the cladding 16, provided between the step core portion 12 and the cladding 16.
FIG. 5(d) is a variant example of the segment core type refractive index profile shown in FIG. 5(b). A core 24 is formed with a low refractive index portion 25, which has a lower refractive index than the cladding 26, provided between the ring core portion 23 and the cladding 26.
However, in conventionally proposed dispersion shifted optical fibers under the preconditions that essentially the transmission path be single mode and that bending loss be held to 100 dB/m or less, it has been difficult to achieve both an enlargement in the effective core area and a reduction in the dispersion slope.
For example, in the examples having the refractive index profiles shown in FIGS. 5(a) to 5(d), if an attempt is made to increase the effective core area by 90 xcexcm2 or more it is not possible to be dispersion slope enough small.
The present invention was conceived in view of the above and it is an object thereof to provide a dispersion shifted optical fiber that fulfills the conditions of being essentially single mode and having bending loss of less than 100 dB/m, and also enables sufficient enlargement of the effective core area and sufficient reduction of the dispersion slope to be achieved.
In order to achieve the above objects, the first aspect of the present invention is a dispersion shifted optical fiber comprising a core and cladding provided at an outer periphery of the core, and having a refractive index profile in which the core is provided with a central core portion and a peripheral core portion having a higher refractive index than the central core portion provided at an outer periphery of the central core portion, and the cladding has a lower refractive index than the peripheral core portion, wherein, in a used wavelength band selected from 1490 to 1625 nm, the dispersion shifted optical fiber has an effective core area of 45 to 130 xcexcm2, a chromatic dispersion value of xe2x88x928 to +8 ps/km/nm, a dispersion slope of 0.12 ps/km/nm2 or less, a bending loss of 100 dB/m or less, and a cutoff wavelength that provides essentially single mode propagation.
The second aspect of the present invention is the dispersion shifted optical fiber according to the first aspect, wherein a core comprises a central core portion and a peripheral core portion, and if xcex941 is a relative refractive index difference of the central core when the refractive index of the cladding is taken as a reference, and xcex942 is a relative refractive index difference of the peripheral core portion when the refractive index of the cladding is taken as the reference, and r1 is a radius of the central core portion and r2 is a radius of the peripheral core portion, then the following conditions a to d are fulfilled:
a: 1.35%xe2x89xa6(xcex942xe2x88x92xcex941)
b: 1.2xe2x89xa6r2/r1xe2x89xa62.0
c: xcex942xe2x89xa70.8% and 1.8xe2x89xa6xcex942xc3x97(r2/r1)2xe2x89xa63.5
d: When the larger one from out of 0.8 or 1.8/(r2/r1)2 is set as xcex942 min, and a ring inner volume is set as xe2x88x92xcex941xc3x97r12, and a ring outer volume is set as xcex942 minxc3x97(r22xe2x88x92r12), then the ring outer volume/ring inner volume is either 2 or more, or 0 or less.
The third aspect of the present invention is the dispersion shifted optical fiber according to the second aspect, wherein, in a used wavelength band selected from 1490 to 1625 nm, the dispersion shifted optical fiber has an effective core area of 75 to 130 xcexcm2, a chromatic dispersion value of xe2x88x926 to +6 ps/km/nm, a dispersion slope of 0.12 ps/km/nm2 or less, a bending loss of 100 dB/m or less, and a cutoff wavelength that provides essentially single mode propagation.
The fourth aspect of the present invention is the dispersion shifted optical fiber according to the second aspect, wherein b and c are within the numerical ranges given below:
b: 1.2xe2x89xa6r2/r1xe2x89xa61.9
c: xcex942xe2x89xa70.8% and 1.8xe2x89xa6xcex942xc3x97(r2/r1)2xe2x89xa63.2.
The fifth aspect of the present invention is the dispersion shifted optical fiber according to the fourth aspect, wherein the effective core area is 85 to 130 xcexcm2.
The sixth aspect of the present invention is the dispersion shifted optical fiber according to the second aspect, wherein b and c are within the numerical ranges given below:
b: 1.2xe2x89xa6r2/r1xe2x89xa61.8
c: xcex942xe2x89xa70.8% and 1.8xe2x89xa6xcex942xc3x97(r2/r1)2xe2x89xa62.7.
The seventh aspect of the present invention is the dispersion shifted optical fiber according to the sixth aspect, wherein the effective core area is 95 to 130 xcexcm2.
The eighth aspect of the present invention is the dispersion shifted optical fiber according to the second aspect, wherein r2/r1 is 1.3 or more and xcex941 is 0% or less.
The ninth aspect of the present invention is the dispersion shifted optical fiber according to the eighth aspect, wherein the dispersion slope is 0.10 ps/km/nm2 or less.
The tenth aspect of the present invention is the dispersion shifted optical fiber according to the first aspect, wherein the core comprises a central core portion and a peripheral core portion, and in a used wavelength band selected from 1490 to 1625 nm, the dispersion shifted optical fiber has an effective core area of 45 to 70 xcexcm2, a chromatic dispersion value of xe2x88x926 to +6 ps/km/nm, a dispersion slope of 0.05 to 0.08 ps/km/nm2, a bending loss of 100 dB/m or less, and a cutoff wavelength that provides essentially single mode propagation.
The eleventh aspect of the present invention is the dispersion shifted optical fiber according to tenth aspect, wherein, if xcex941 is a relative refractive index difference of the central core when the refractive index of the cladding is taken as a reference, and xcex942 is a relative refractive index difference of the peripheral core portion when the refractive index of the cladding is taken as the reference, and r1 is a radius of the central core portion and r2 is a radius of the peripheral core portion, then xcex941 is xe2x88x920.3 to +0.3%, xcex942 is 0.8% or more, and r2/r1 is 1.4 to 2.5.
The twelfth aspect of the present invention is the dispersion shifted optical fiber according to the tenth aspect, wherein xcex941 is 0%.
The thirteenth aspect of the present invention is the dispersion shifted optical fiber according to the first aspect, wherein the core comprises a peripheral core portion, a second ring portion, and a third ring portion provided in that order on the central core portion and when the relative refractive index difference and radius of the central core portion, the peripheral core portion, the second ring portion, and the third core portion are set respectively as (xcex941, r1), (xcex942, r2), (xcex943, r3), and (xcex944, r4) when the cladding is taken as a reference, then the dispersion shifted optical fiber has a refractive index profile in which xcex941 and xcex943 are set as negative values, xcex942 is set as a positive value, and xcex944 is set as 0 or more, and in a used wavelength band selected from 1490 to 1625 nm, the dispersion shifted optical fiber has an effective core area of 45 to 120 xcexcm2, a dispersion slope of 0.03 to 0.10 ps/km/nm2, a chromatic dispersion absolute value of 0.5 to 8 ps/km/nm, a bending loss of 100 dB/m or less, and a cutoff wavelength that provides essentially single mode propagation.
The fourteenth aspect of the present invention is the dispersion shifted optical fiber according to the thirteenth aspect, wherein the dispersion shifted optical fiber has an effective core area of 50 to 75 xcexcm2 and a dispersion slope of 0.03 to 0.06 ps/km/nm2.
The fifteenth aspect of the present invention is the dispersion shifted optical fiber according to the fourteenth aspect, wherein the chromatic dispersion value is a negative value and xe2x88x920.50%xe2x89xa6xcex941xe2x89xa6xe2x88x920.25%, 0.65%xe2x89xa6xcex942xe2x89xa60.85%, xe2x88x920.50%xe2x89xa6xcex943xe2x89xa6xe2x88x920.25%, 0.0%xe2x89xa6xcex944xe2x89xa60.30%, 1.5xe2x89xa6r2/r1xe2x89xa62.5, 1.5xe2x89xa6(r3xe2x88x92r2)/r1xe2x89xa62.5, 0.5xe2x89xa6(r4xe2x88x92r3)/r2xe2x89xa62.0.
The sixteenth aspect of the present invention is the dispersion shifted optical fiber according to the fourteenth aspect, wherein the chromatic dispersion value is a positive value and xe2x88x920.5%xe2x89xa6xcex941xe2x89xa6xe2x88x920.05%, 0.75%xe2x89xa6xcex942xe2x89xa60.85%, xe2x88x920.50%xe2x89xa6xcex943xe2x89xa6xe2x88x920.15%, 0.0%xe2x89xa6xcex944xe2x89xa60.3%, 1.5xe2x89xa6r2/r1xe2x89xa62.5, 1.5xe2x89xa6(r3xe2x88x92r2)/r1xe2x89xa62.5, 0.5xe2x89xa6(r4xe2x88x92r3)/r2xe2x89xa62.0.
The seventeenth aspect of the present invention is the dispersion shifted optical fiber according to the thirteenth aspect, wherein the dispersion shifted optical fiber has an effective core area of 75 to 100 xcexcm2 and a dispersion slope of 0.06 to 0.09 ps/km/nm2.
The eighteenth aspect of the present invention is the dispersion shifted optical fiber according to the seventeenth aspect, wherein the chromatic dispersion value is a negative value and xe2x88x920.50%xe2x89xa6xcex941xe2x89xa6xe2x88x920.20%, 0.65%xe2x89xa6xcex942xe2x89xa60.85%, xe2x88x920.50%xe2x89xa6xcex943xe2x89xa6xe2x88x920.25%, 0.0%xe2x89xa6xcex944xe2x89xa60.30%, 1.3xe2x89xa6r2/r1xe2x89xa62.5, 0.5xe2x89xa6(r3xe2x88x92r2)/r1xe2x89xa61.5, 0.5xe2x89xa6(r4xe2x88x92r3)/r2xe2x89xa62.0.
The nineteenth aspect of the present invention is the dispersion shifted optical fiber according to the seventeenth aspect, wherein the chromatic dispersion value is a positive value and xe2x88x920.50%xe2x89xa6xcex941xe2x89xa6xe2x88x920.05%, 0.65%xe2x89xa6xcex942xe2x89xa60.85%, xe2x88x920.50%xe2x89xa6xcex943xe2x89xa6xe2x88x920.15%, 0.0%xe2x89xa6xcex944xe2x89xa60.30%, 1.3xe2x89xa6r2/r1xe2x89xa63.0, 0.5xe2x89xa6(r3xe2x88x92r2)/r1xe2x89xa62.5, 0.5xe2x89xa6(r4xe2x88x92r3)/r2xe2x89xa62.0.
The twentieth aspect of the present invention is the dispersion shifted optical fiber according to the thirteenth aspect, wherein the dispersion shifted optical fiber has an effective core area of 100 to 120 xcexcm2 and a dispersion slope of 0.08 to 0.10 ps/km/nm2.
The twenty first aspect of the present invention is the dispersion shifted optical fiber according to the twentieth aspect, wherein the chromatic dispersion value is a positive value and xe2x88x920.50%xe2x89xa6xcex941xe2x89xa6xe2x88x920.25%, 0.65%xe2x89xa6xcex942xe2x89xa60.75%, xe2x88x920.50%xe2x89xa6xcex943xe2x89xa6xe2x88x920.25%, 0.0%xe2x89xa6xcex944xe2x89xa60.30%, 1.3xe2x89xa6r2/r1xe2x89xa62.5, 0.5xe2x89xa6(r3xe2x88x92r2)/r1xe2x89xa61.5, 0.5xe2x89xa6(r4xe2x88x92r3)/r2xe2x89xa62.0.